802.11 Wireless Network Site Surveying and Installation

Cables 45

But as the tournament started and many users were added, they encountered difficulty.

When the first users (clients on the front nine of the course) registered to the AP, the AP

sampled both antennas (one at a time) and selected the antenna pointing to the front section.

When users started migrating to the back nine, and more users entered the front nine,

problems started popping up. As the AP was communicating to the users on the front

section of the course users on the back section could not hear that RF traffic because the

back-nine antenna was being used at that instant. Therefore, the back users tried to send

their own traffic, which was not heard by the AP.

In the case of the golf course, two methods could resolve this problem. One method is to

replace the directional Yagi antenna with a similar-gain omni antenna. The AP’s radio

would then be able to work in all directions rather than the limited directional pattern of the

Yagi.

Another method is to add an AP to cover the other radio cell. This way both APs could

properly handle the RF traffic, and each AP could use the higher-gain Yagi antenna to cover

each area.

Connectors

To prevent improper usage of antennas that can create interference or violate the U.S.

regulations, the FCC added a regulation requiring connectors used on WLAN equipment

manufactured after June 1994 to be of a “unique and non-standard” format. Canada

followed suit with a similar regulation. Most WLAN vendors such as Cisco worked with

connector companies to produce connectors that, while maintaining a quality 50-ohm low-

loss connection, met this regulation. Several companies started using a version of the

popular TNC (threaded Neill-Concelman) connector that has a center conductor compo-

nent reversed between the plug and jack of a regular TNC connector. This is known as a

reverse-polarity TNC (RP-TNC). Although they are similar to the standard TNC

connectors, they cannot be mated with a standard connector. Therefore, you need to verify

that all components you are purchasing (antennas, cables, and so on) are supplied with the

same connector format.

Cables

The antenna should be mounted at a location that utilizes its radiation pattern to maximum

performance for the users. In some cases, this is not an ideal location to mount the AP.

Therefore, it is sometimes desired to separate the antenna from the AP or radio device. This

can be due to the necessity to mount the antenna outdoors and keep the AP indoors, or to

mount the AP in the ceiling and mount the antenna below the ceiling. Sometimes customers

may even want to keep the AP in a wiring closet and place the antenna out in the user area.